Acoustic echo cancellation device, acoustic echo cancellation method and non-transitory computer readable recording medium recording acoustic echo cancellation program

ABSTRACT

An acoustic echo cancellation device includes: a first echo canceller which, using an input signal obtained from at least two microphones and a reproduced signal outputted to a speaker, produces a first pseudo echo signal which indicates a component of the reproduced signal contained in the input signal; and a second echo canceller which, using at least one input signal outputted from the at least two microphones and the first pseudo echo signal, produces a second pseudo echo signal which indicates a component of the first pseudo echo signal contained in the at least one input signal, and cancels an acoustic echo component of the at least one input signal using the second pseudo echo signal.

FIELD OF THE INVENTION

This disclosure relates to an acoustic echo cancellation device, anacoustic echo cancellation method, and a non-transitory computerreadable recording medium recording an acoustic echo cancellationprogram that cancel an acoustic echo component of an input signaloutputted from a microphone.

BACKGROUND ART

Conventionally, there has been known a microphonic two-way conversationsystem using a microphone and a speaker. In such a microphonic two-wayconversation system, a voice which a talker on a sender side utters isinputted to a microphone on the sender side, is transmitted to equipmenton the receiver side via a communication line as a sender signal, and isreproduced by a speaker on the receiver side. A voice reproduced by thespeaker on the receiver side propagates a space on the receiver side, isinputted to a microphone on the receiver side, and is transmitted to thesender side. In such an operation, from the speaker on the sender side,a voice which a talker himself/herself utters and is transmitted througha lapse of a time during which the voice passes via the communicationline and a time during which the voice propagates in a space on areceiver side is reproduced. The voice which propagates from the speakeron the receiver side to the microphone is referred to as an acousticecho and brings about the deterioration of conversation quality.

Accordingly, in the microphonic two-way conversation system, an echocanceller which suppresses an acoustic echo is used.

Further, recently, to provide a more natural conversation environment,the development of a microphonic two-way conversation system which usesa plurality of microphones is underway (see JP 5826712 B2, for example).

However, in the above-mentioned prior art, it is difficult to reduce anarithmetic amount for removing an acoustic echo while maintaining aconversation performance. Accordingly, there is still a room forimprovement.

SUMMARY OF THE INVENTION

This disclosure is provided for overcoming the above-mentioneddrawbacks, and it is an object of this disclosure to provide an acousticecho cancellation device, an acoustic echo cancellation method, and anon-transitory computer readable recording medium recording an acousticecho cancellation program which can maintain a conversation performanceand can reduce an arithmetic amount for removing an acoustic echo.

According to an aspect of this disclosure, there is provided an acousticecho cancellation device including: a first echo canceller which, usingan input signal obtained from at least two microphones and a reproducedsignal outputted to a speaker, produces a first pseudo echo signal whichindicates a component of the reproduced signal contained in the inputsignal; and a second echo canceller which, using at least one inputsignal outputted from the at least two microphones and the first pseudoecho signal produced by the first echo canceller, produces a secondpseudo echo signal which indicates a component of the first pseudo echosignal contained in the at least one input signal, and cancels anacoustic echo component of the at least one input signal using theproduced second pseudo echo signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing a configuration of a conversation deviceaccording to a first embodiment of this disclosure;

FIG. 2 is a flowchart for describing an operation of an acoustic echocancellation device according to the first embodiment of thisdisclosure;

FIG. 3 is a view showing a configuration of a conversation deviceaccording to a modification 1 of the first embodiment of thisdisclosure;

FIG. 4 is a view showing a configuration of a conversation deviceaccording to a second embodiment of this disclosure;

FIG. 5 is a flowchart for describing an operation of an acoustic echocancellation device according to the second embodiment of thisdisclosure;

FIG. 6 is a view showing the configuration of a conversation deviceaccording to a modification of the second embodiment of this disclosure;

FIG. 7 is a view showing a configuration of a conversation deviceaccording to a third embodiment of this disclosure;

FIG. 8 is a flowchart for describing an operation of an acoustic echocancellation device according to the third embodiment of thisdisclosure;

FIG. 9 is a view showing a configuration of a conversation deviceaccording to a modification of the third embodiment of this disclosure;and

FIG. 10 is a view showing a configuration of a conversation deviceaccording to a modification 2 of the first embodiment of thisdisclosure.

DESCRIPTION OF EMBODIMENTS

(Finding on which this Disclosure is Based)

In a microphonic conversation system where a plurality of microphonesare used, an echo canceller becomes necessary for each microphone.Accordingly, the number of echo cancellers is also increasedcorresponding to the number of microphones and hence, a total arithmeticamount of the plurality of echo cancellers is increased.

The above-mentioned conventional multi-channel echo cancellation devicehas the same number of echo replica generating part as the microphones,and each of the echo replica generating parts has the sameconfiguration. Accordingly, as the number of microphones is increased,the number of echo replica generating parts is also increased thusgiving rise to a concern that an arithmetic amount for removing anacoustic echo is also increased.

In the above-mentioned conventional multi-channel echo cancellationdevice, by limiting echo replica producing processing and updatingprocessing of an adaptive filter coefficient within an effectivefrequency domain, an arithmetic amount is reduced as a whole in amulti-channel microphonic conversation system formed of a large numberof speakers and microphones.

However, in the conventional multi-channel echo cancellation device, thefrequency domain of the echo replica generating part is limited andhence, a frequency domain which is not learned is generated thus givingrise to a concern that the limitation of the frequency domain becomes afactor of deteriorating a conversation performance.

To overcome the above-mentioned drawbacks, an acoustic echo cancellationdevice according to an aspect of this disclosure includes: a first echocanceller which, using an input signal obtained from at least twomicrophones and a reproduced signal outputted to a speaker, produces afirst pseudo echo signal which indicates a component of the reproducedsignal contained in the input signal; and a second echo canceller which,using at least one input signal outputted from the at least twomicrophones and the first pseudo echo signal produced by the first echocanceller, produces a second pseudo echo signal which indicates acomponent of the first pseudo echo signal contained in the at least oneinput signal, and cancels an acoustic echo component of the at least oneinput signal using the produced second pseudo echo signal.

With such a configuration, the second pseudo echo signal is producedusing the already produced first pseudo echo signal. Accordingly, afilter length (tap length) of an adaptive filter used in producing thesecond pseudo echo signal can be shortened and hence, a conversationperformance can be maintained and, at the same time, an arithmeticamount for removing an acoustic echo can be reduced.

The above-mentioned acoustic echo cancellation device may furtherinclude a delay part which delays at least one input signal outputtedfrom the at least two microphones. The second echo canceller may producea second pseudo echo signal which indicates a component of the firstpseudo echo signal contained in the at least one delayed input signalusing the at least one delayed input signal and the first pseudo echosignal produced by the first echo canceller, and may cancel an acousticecho component of the at least one delayed input signal using theproduced second pseudo echo signal.

With such a configuration, at least one input signal inputted to thesecond echo canceller is delayed and hence, a time difference betweenthe first pseudo echo signal produced by the first echo canceller andthe at least one input signal is eliminated whereby the second pseudoecho signal can be produced with certainty.

In the above-mentioned acoustic echo cancellation device, the at leasttwo microphones may include a first microphone which outputs a firstinput signal, and a second microphone which outputs a second inputsignal, the delay part may include a first delay part which delays thefirst input signal and a second delay part which delays the second inputsignal. The acoustic echo cancellation device may further include anadder which adds the first input signal and the second input signal toeach other. The first echo canceller may produce the first pseudo echosignal which indicates a component of the reproduced signal contained inan addition signal using the addition signal from the adder and thereproduced signal. The second echo canceller may include: a third echocanceller which produces a third pseudo echo signal which indicates acomponent of the first pseudo echo signal contained in the delayed firstinput signal using the delayed first input signal and the first pseudoecho signal produced by the first echo canceller, and cancels anacoustic echo component of the delayed first input signal using theproduced third pseudo echo signal; and a fourth echo canceller whichproduces a fourth pseudo echo signal which indicates a component of thefirst pseudo echo signal contained in the delayed second input signalusing the delayed second input signal and the first pseudo echo signalproduced by the first echo canceller, and cancels an acoustic echocomponent of the delayed second input signal using the produced fourthpseudo echo signal.

With such a configuration, the first input signal inputted to the thirdecho canceller is delayed and, at the same time, the second input signalinputted to the fourth echo canceller is delayed. Accordingly, a timedifference between the first pseudo echo signal produced by the firstecho canceller and the first input signal is eliminated, and a timedifference between the first pseudo echo signal and the second inputsignal is eliminated and hence, it is possible to produce the thirdpseudo echo signal and the fourth pseudo echo signal with certainty.

In the above-mentioned acoustic echo cancellation device, the at leasttwo microphones may include a first microphone which outputs a firstinput signal, and a second microphone which outputs a second inputsignal. The acoustic echo cancellation device may further include anadder which adds the first input signal and the second input signal toeach other. The first echo canceller may produce the first pseudo echosignal which indicates a component of the reproduced signal contained inan addition signal using the addition signal from the adder and thereproduced signal. The second echo canceller may include: a third echocanceller which produces a third pseudo echo signal which indicates acomponent of the first pseudo echo signal contained in the first inputsignal using the first input signal and the first pseudo echo signalproduced by the first echo canceller, and cancels an acoustic echocomponent of the first input signal using the produced third pseudo echosignal; and a fourth echo canceller which produces a fourth pseudo echosignal which indicates a component of the first pseudo echo signalcontained in the second input signal using the second input signal andthe first pseudo echo signal produced by the first echo canceller, andcancels an acoustic echo component of the second input signal using theproduced fourth pseudo echo signal.

In such a configuration, the arrangement positions of at least twomicrophones differ from each other. Accordingly, a waveform of areflected wave (echo signal) inputted as an acoustic echo differsbetween the microphones. In the case where a phase of an echo signal isopposite to a phase of an input signal which is a voice of a talker,when the echo signal is added to the input signal, the input signal iseliminated. Accordingly, it is difficult to cancel an acoustic echo ofthe input signal. However, a first input signal and a second inputsignal from at least two microphones are added and hence, an effect ofloss of a signal caused by interference of acoustic echoes can bereduced.

In the above-mentioned acoustic echo cancellation device, the at leasttwo microphones may include a first microphone which outputs a firstinput signal, and a second microphone which outputs a second inputsignal, the first echo canceller may produce the first pseudo echosignal which indicates a component of the reproduced signal contained inthe first input signal using the first input signal and the reproducedsignal, and cancel an acoustic echo component of the first input signalusing the produced first pseudo echo signal, and the second echocanceller may produce a second pseudo echo signal which indicates acomponent of the first pseudo echo signal contained in the second inputsignal using the second input signal and the first pseudo echo signalproduced by the first echo canceller, and cancel an acoustic echocomponent of the second input signal using the produced second pseudoecho signal.

With such a configuration, the second pseudo echo signal is producedusing the already produced first pseudo echo signal. Accordingly, afilter length (tap length) of an adaptive filter used in producing thesecond pseudo echo signal can be shortened and hence, a conversationperformance can be maintained and, at the same time, an arithmeticamount for removing an acoustic echo can be reduced.

In the above-mentioned acoustic echo cancellation device, the at leasttwo microphones may include a first microphone which outputs a firstinput signal, and a second microphone which outputs a second inputsignal, the first echo canceller may include: a first calculation partthat calculates a first error signal which indicates an error betweenthe first input signal and the first pseudo echo signal; a secondcalculation part that calculates a second error signal which indicatesan error between the second input signal and the first pseudo echosignal; an averaging processing part that averages an addition signalobtained by adding the first error signal and the second error signal toeach other; and a producing part that produces the first pseudo echosignal which indicates a component of the reproduced signal contained inan average signal using the average signal from the averaging processingpart and the reproduced signal, and the second echo canceller mayinclude: a third echo canceller which produces a third pseudo echosignal which indicates a component of the first pseudo echo signalcontained in the first input signal using the first input signal and thefirst pseudo echo signal produced by the first echo canceller, andcancels an acoustic echo component of the first input signal using theproduced third pseudo echo signal; and a fourth echo canceller whichproduces a fourth pseudo echo signal which indicates a component of thefirst pseudo echo signal contained in the second input signal using thesecond input signal and the first pseudo echo signal produced by thefirst echo canceller, and cancels an acoustic echo component of thesecond input signal using the produced fourth pseudo echo signal.

In such a configuration, the arrangement positions of at least twomicrophones differ from each other. Accordingly, a waveform of areflected wave (echo signal) inputted as an acoustic echo differsbetween the microphones. In the case where a phase of an echo signal isopposite to a phase of an input signal which is a voice of a talker,when the echo signal is added to the input signal, the input signal iseliminated. Accordingly, it is difficult to cancel an acoustic echo ofthe input signal. However, the error signals of the first input signaland the second input signal from at least two microphones are added toeach other and are averaged and hence, an effect of loss of a signalcaused by interference of acoustic echoes can be reduced.

Further, the above-mentioned acoustic echo cancellation device mayfurther include: a first converting part that converts the input signalin a time domain into an input signal in a frequency domain; a secondconverting part that converts the reproduced signal in a time domaininto a reproduced signal in a frequency domain; a third converting partthat converts the at least one input signal in a time domain into atleast one input signal in a frequency domain; and a fourth convertingpart that converts the first pseudo echo signal in a time domain into afirst pseudo echo signal in a frequency domain.

With such a configuration, the first echo canceller and the second echocanceller can produce a first pseudo echo signal and a second pseudoecho signal using an adaptive algorithm in a frequency domain, and aconvolution operation can be executed by multiplication and hence, anarithmetic amount can be further reduced.

In the above-mentioned acoustic echo cancellation device, a filterlength of the second echo canceller may be shorter than a filter lengthof the first echo canceller.

With such a configuration, an arithmetic amount for removing an acousticecho in the second echo canceller can be reduced.

In the above-mentioned acoustic echo cancellation device, the first echocanceller may produce the first pseudo echo signal with respect to themicrophone disposed at the position closest to the speaker.

With such a configuration, a first pseudo echo signal which indicates acomponent of a reproduced signal contained in an input signal isproduced using an input signal outputted from the microphone disposed atthe position closest to the speaker and the reproduced signal, and asecond pseudo echo signal is produced using the produced first pseudoecho signal. Accordingly, a filter length (tap length) of an adaptivefilter used in producing the second pseudo echo signal can be shortened.

An acoustic echo cancellation method according to another aspect of thisdisclosure is an acoustic echo cancellation method in an acoustic echocancellation device which cancels an acoustic echo component of an inputsignal outputted from a microphone, the method including: a step ofproducing a first pseudo echo signal which indicates a component of areproduced signal contained in the input signal using an input signalobtained from the at least two microphones and the reproduced signaloutputted to a speaker; a step of producing a second pseudo echo signalwhich indicates a component of the first pseudo echo signal contained inthe at least one input signal using the at least one input signaloutputted from the at least two microphones and the first pseudo echosignal produced by the first echo canceller; and a step of cancelling anacoustic echo component of the at least one input signal using theproduced second pseudo echo signal.

With such a configuration, the second pseudo echo signal is producedusing the already produced first pseudo echo signal. Accordingly, afilter length (tap length) of an adaptive filter used in producing thesecond pseudo echo signal can be shortened and hence, a conversationperformance can be maintained and, at the same time, an arithmeticamount for removing an acoustic echo can be reduced.

A non-transitory computer readable recording medium recording anacoustic echo cancellation program according to another aspect of thisdisclosure allows a computer to function as: a first echo cancellerwhich, using an input signal obtained from at least two microphones anda reproduced signal outputted to a speaker, produces a first pseudo echosignal which indicates a component of the reproduced signal contained inthe input signal; and a second echo canceller which, using at least oneinput signal outputted from the at least two microphones and the firstpseudo echo signal produced by the first echo canceller, produces asecond pseudo echo signal which indicates a component of the firstpseudo echo signal contained in the at least one input signal, andcancels an acoustic echo component of the at least one input signalusing the produced second pseudo echo signal.

With such a configuration, the second pseudo echo signal is producedusing the already produced first pseudo echo signal. Accordingly, afilter length (tap length) of an adaptive filter used in producing thesecond pseudo echo signal can be shortened and hence, a conversationperformance can be maintained and, at the same time, an arithmeticamount for removing an acoustic echo can be reduced.

Hereinafter, embodiments of this disclosure are described with referenceto attached drawings. The embodiments described hereinafter form oneexample which embodies this disclosure and are not intended to limit thetechnical scope of this disclosure.

First Embodiment

FIG. 1 is a view showing the configuration of a conversation deviceaccording to the first embodiment of this disclosure. The conversationdevice is used as a microphonic hand free conversation system mounted onan automobile or the like, a microphonic two-way communicationconference system, an interphone system, and the like.

The conversation device shown in FIG. 1 includes an acoustic echocancellation device 1, a first microphone 11, a second microphone 12, aninput terminal 14, a speaker 15, a first output terminal 20, and asecond output terminal 21.

The first microphone 11 and the second microphone 12 are disposed in aspace where a talker is present, and collects a voice of the talker. Thefirst microphone 11 outputs a first input signal which indicates thecollected voice, to the acoustic echo cancellation device 1. The secondmicrophone 12 outputs a second input signal which indicates thecollected voice, to the acoustic echo cancellation device 1.

The input terminal 14 outputs a reproduced signal received from aconversation device on a receiver side (not shown in the drawings) tothe acoustic echo cancellation device 1 and the speaker 15.

The speaker 15 outputs the inputted reproduced signal to the outside.When a voice outputted from the speaker 15 is collected by the firstmicrophone 11 and the second microphone 12, the voice uttered by atalker on the receiver side is reproduced from the speaker on thereceiver side with a delay. As a result, a so-called acoustic echo isgenerated. In view of the above, the acoustic echo cancellation device 1cancels acoustic echo components of the first input signal and thesecond input signal outputted from the first microphone 11 and thesecond microphone 12.

The first output terminal 20 outputs the first input signal in which theacoustic echo component is cancelled by the acoustic echo cancellationdevice 1. The second output terminal 21 outputs the second input signalin which the acoustic echo component is cancelled by the acoustic echocancellation device 1.

The input terminal 14, the first output terminal 20, and the secondoutput terminal 21 are connected to a communication part (not shown inthe drawings). The communication part transmits the first input signaland the second input signal to the conversation device on the receiverside (not shown in the drawings) via a network, and receives thereproduced signal from the conversation device on the receiver side (notshown in the drawings) via the network. The network is, for example, theInternet.

The acoustic echo cancellation device 1 includes an adder 13, a firstecho canceller 16, and a second echo canceller 17.

The adder 13 adds the first input signal from the first microphone 11and the second input signal from the second microphone 12 to each other.

The first echo canceller 16 produces a first pseudo echo signal whichindicates a component of the reproduced signal contained in the inputsignal using the input signal obtained from at least two microphones andthe reproduced signal outputted to the speaker.

In the first embodiment, an input signal obtained from at least twomicrophones is an addition signal obtained by adding the first inputsignal from the first microphone 11 and the second input signal from thesecond microphone 12 to each other. That is, the first echo canceller 16produces a first pseudo echo signal which indicates a component of thereproduced signal contained in the addition signal using the additionsignal from the adder 13 and the reproduced signal.

The first echo canceller 16 includes an adaptive filter 161 and an errorcalculation part 162.

The adaptive filter 161 produces a first pseudo echo signal whichindicates a component of the reproduced signal contained in the additionsignal by convoluting the filter coefficient and the reproduced signal.

The error calculation part 162 calculates an error signal between anaddition signal from the adder 13 and the first pseudo echo signal fromthe adaptive filter 161, and outputs the calculated error signal to theadaptive filter 161. The adaptive filter 161 modifies a filtercoefficient based on the inputted error signal, and produces the firstpseudo echo signal by convoluting the modified filter coefficient andthe reproduced signal. The adaptive filter 161 modifies the filtercoefficient such that the error signal is minimized using the adaptivealgorithm. As the adaptive algorithm, for example, a normalized leastmean square (NLMS) method, an affine projection (AP) method, or arecursive least square (RLS) method can be used.

The second echo canceller 17 produces a second pseudo echo signal whichindicates a component of the first pseudo echo signal contained in atleast one input signal using at least one input signal outputted from atleast two microphones and the first pseudo echo signal produced by thefirst echo canceller 16, and cancels an acoustic echo component of atleast one input signal using the produced second pseudo echo signal.

The second echo canceller 17 includes: a third echo canceller 18 whichcancels an acoustic echo component of the first input signal; and afourth echo canceller 19 which cancels an acoustic echo component of thesecond input signal. The first pseudo echo signal produced by the firstecho canceller 16 is outputted to the third echo canceller 18 and thefourth echo canceller 19.

The third echo canceller 18 produces a third pseudo echo signal whichindicates a component of the first pseudo echo signal contained in thefirst input signal using the first input signal and the first pseudoecho signal produced by the first echo canceller 16, and cancels anacoustic echo component of the first input signal using the producedthird pseudo echo signal.

The third echo canceller 18 includes an adaptive filter 181 and an errorcalculation part 182.

The adaptive filter 181 produces a third pseudo echo signal whichindicates a component of the first pseudo echo signal contained in thefirst input signal by convoluting a filter coefficient and the firstpseudo echo signal.

The error calculation part 182 calculates an error signal between thefirst input signal from the first microphone 11 and the third pseudoecho signal from the adaptive filter 181, and outputs the calculatederror signal to the adaptive filter 181. The adaptive filter 181modifies a filter coefficient based on the inputted error signal, andproduces the third pseudo echo signal by convoluting the modified filtercoefficient and the first pseudo echo signal. The adaptive filter 181modifies the filter coefficient such that the error signal is minimizedusing the adaptive algorithm. As the adaptive algorithm, for example, anNLMS method, an AP method, or an RLS method can be used.

The error calculation part 182 cancels an acoustic echo component fromthe first input signal by subtracting the third pseudo echo signal fromthe adaptive filter 181 from the first input signal from the firstmicrophone 11. Accordingly, the error calculation part 182 outputs thefirst input signal in which the acoustic echo component is cancelled tothe first output terminal 20.

The fourth echo canceller 19 produces a fourth pseudo echo signal whichindicates a component of the first pseudo echo signal contained in thesecond input signal using the second input signal and the first pseudoecho signal produced by the first echo canceller 16, and cancels anacoustic echo component of the second input signal using the producedfourth pseudo echo signal.

The fourth echo canceller 19 includes an adaptive filter 191 and anerror calculation part 192.

The adaptive filter 191 produces a fourth pseudo echo signal whichindicates a component of the first pseudo echo signal contained in thesecond input signal by convoluting a filter coefficient and the firstpseudo echo signal.

The error calculation part 192 calculates an error signal between thesecond input signal from the second microphone 12 and the fourth pseudoecho signal from the adaptive filter 191, and outputs the calculatederror signal to the adaptive filter 191. The adaptive filter 191modifies a filter coefficient based on the inputted error signal, andproduces the fourth pseudo echo signal by convoluting the modifiedfilter coefficient and the first pseudo echo signal. The adaptive filter191 modifies the filter coefficient such that the error signal isminimized using the adaptive algorithm. As the adaptive algorithm, forexample, an NLMS method, an AP method, or an RLS method can be used.

The error calculation part 192 cancels an acoustic echo component fromthe second input signal by subtracting the fourth pseudo echo signalfrom the adaptive filter 191 from the second input signal from thesecond microphone 12. Accordingly, the error calculation part 192outputs the second input signal in which the acoustic echo component iscancelled to the second output terminal 21.

In the first embodiment, a filter length of the second echo canceller 17is shorter than a filter length of the first echo canceller 16. That is,a filter length of the adaptive filter 181 of the third echo canceller18 is shorter than a filter length of the adaptive filter 161 of thefirst echo canceller 16, and a filter length of the adaptive filter 191of the fourth echo canceller 19 is shorter than a filter length of theadaptive filter 161 of the first echo canceller 16.

In the first embodiment, the conversation device includes twomicrophones. However, this disclosure is not particularly limited tosuch a case, and the conversation device may include three or moremicrophones. When the conversation device includes three or moremicrophones, the adder 13 adds respective input signals from three ormore microphones, and the first echo canceller 16 outputs the firstpseudo echo signal to echo cancellers which are provided to therespective three or more microphones.

In the first embodiment, the conversation device includes one speaker.However, this disclosure is not particularly limited to such a case, andthe conversation device may include two or more speakers. In the casewhere the conversation device includes a plurality of speakers, it isnecessary for the conversation device to include the same number ofacoustic echo cancellation devices 1 as the plurality of speakers.

Next, an operation of the acoustic echo cancellation device 1 accordingto the first embodiment of this disclosure is described.

FIG. 2 is a flowchart for describing an operation of the acoustic echocancellation device according to the first embodiment of thisdisclosure.

In step S1, the adder 13 adds a first input signal from the firstmicrophone 11 and a second input signal from the second microphone 12 toeach other. Due to such an operation, the first input signal from thefirst microphone 11 and the second input signal from the secondmicrophone 12 are inputted to the adder 13.

Next, in step S2, the adaptive filter 161 of the first echo canceller 16produces a first pseudo echo signal which indicates a component of areproduced signal contained in an addition signal by convoluting afilter coefficient and the reproduced signal.

Next, in step S3, the error calculation part 162 calculates an errorsignal between the addition signal from the adder 13 and the firstpseudo echo signal from the adaptive filter 161 by subtracting the firstpseudo echo signal from the addition signal. The error calculation part162 outputs the calculated error signal to the adaptive filter 161.

Next, in step S4, the adaptive filter 161 modifies a filter coefficientbased on the error signal inputted from the error calculation part 162.The adaptive filter 161 produces the first pseudo echo signal byconvoluting the modified filter coefficient and the reproduced signal.

Next, in step S5, the adaptive filter 161 outputs the produced firstpseudo echo signal to the third echo canceller 18 and the fourth echocanceller 19.

Next, in step S6, the adaptive filter 181 of the third echo canceller 18produces a third pseudo echo signal which indicates a component of thefirst pseudo echo signal contained in the first input signal byconvoluting the filter coefficient and the first pseudo echo signal.

Next, in step S7, the error calculation part 182 calculates an errorsignal between the first input signal from the first microphone 11 andthe third pseudo echo signal from the adaptive filter 181 by subtractingthe third pseudo echo signal from the first input signal. The errorcalculation part 182 outputs the calculated error signal to the adaptivefilter 181.

Next, in step S8, the adaptive filter 181 modifies a filter coefficientbased on the error signal inputted from the error calculation part 182.The adaptive filter 181 produces the third pseudo echo signal byconvoluting the modified filter coefficient and the first pseudo echosignal.

Next, in step S9, the error calculation part 182 outputs the first inputsignal in which the acoustic echo component is cancelled to the firstoutput terminal 20. That is, the error calculation part 182 cancels anacoustic echo component from the first input signal by subtracting thethird pseudo echo signal from the adaptive filter 181 from the firstinput signal from the first microphone 11.

Next, in step S10, the adaptive filter 191 of the fourth echo canceller19 produces a fourth pseudo echo signal which indicates a component ofthe first pseudo echo signal contained in the second input signal byconvoluting the filter coefficient and the first pseudo echo signal.

Next, in step S11, the error calculation part 192 calculates an errorsignal between the second input signal from the second microphone 12 andthe fourth pseudo echo signal from the adaptive filter 191 bysubtracting the fourth pseudo echo signal from the second input signal.The error calculation part 192 outputs the calculated error signal tothe adaptive filter 191.

Next, in step S12, the adaptive filter 191 modifies a filter coefficientbased on the error signal inputted from the error calculation part 192.The adaptive filter 191 produces the fourth pseudo echo signal byconvoluting the modified filter coefficient and the first pseudo echosignal.

Next, in step S13, the error calculation part 192 outputs the secondinput signal in which the acoustic echo component is cancelled to thesecond output terminal 21. That is, the error calculation part 192cancels an acoustic echo component from the second input signal bysubtracting the fourth pseudo echo signal from the adaptive filter 191from the second input signal from the second microphone 12.

In an initial stage where the acoustic echo cancellation device 1 startsits operation, the filter coefficient is not sufficiently modified.Accordingly, an acoustic echo component cannot be sufficiently cancelledfrom the first input signal and the second input signal. However, byrepeatedly performing processing in step S1 to step S13, the filtercoefficient is sufficiently modified and hence, the acoustic echocomponent can be sufficiently cancelled from the first input signal andthe second input signal.

In this manner, the first echo canceller 16 produces the first pseudoecho signal which indicates a component of the reproduced signalcontained in the input signals obtained from at least two microphones,and the second echo canceller 17 produces a second pseudo echo signalwhich indicates a component of the first pseudo echo signal contained inat least one input signal, and cancels an acoustic echo component of atleast one input signal using the produced second pseudo echo signal.

Accordingly, the second pseudo echo signal is produced using the alreadyproduced first pseudo echo signal. Accordingly, a filter length (taplength) of the adaptive filter used in producing the second pseudo echosignal can be shortened and hence, a conversation performance can bemaintained and, at the same time, an arithmetic amount for removing anacoustic echo can be reduced.

Particularly, echo cancelling processing by the echo canceller on afirst stage (first echo canceller 16) has substantially the same filterlength (arithmetic amount) compared to the prior art. However, echocancelling processing by the echo cancellers on the second stage andsucceeding stages (the third echo canceller 18 and the fourth echocanceller 19) uses the already produced first pseudo echo signal andhence, can have a short filter length compared to the prior art. As aresult, an arithmetic amount can be reduced compared to the prior art.Accordingly, the larger the number of microphone becomes, the smaller anarithmetic amount becomes compared to the prior art.

In the first embodiment, the first echo canceller 16 produces a firstpseudo echo signal using an addition signal obtained by adding a firstinput signal from the first microphone 11 and a second input signal fromthe second microphone 12 and a reproduced signal transmitted to thespeaker 15. In this case, it is considered that an acoustic echoinputted to a virtual microphone disposed at an intermediate positionbetween the first microphone 11 and the second microphone 12 from thespeaker 15 is estimated. The third echo canceller 18 produces a thirdpseudo echo signal using a first pseudo echo signal produced by thefirst echo canceller 16. In this case, it is considered that an acousticecho corresponding to a differential between the position of a virtualmicrophone and the position of the first microphone 11 is estimated.Accordingly, a filter length of the adaptive filter 181 of the thirdecho canceller 18 can be set largely shorter than a filter length of theadaptive filter 161 of the first echo canceller 16. In the same manner,a filter length of the adaptive filter 191 of the fourth echo canceller19 can be set largely shorter than the filter length of the adaptivefilter 161 of the first echo canceller 16.

For example, arithmetic amounts of the third echo canceller 18 and thefourth echo canceller 19 can be reduced to approximately one tenth of anarithmetic amount of the first echo canceller 16. Accordingly, a totalarithmetic amount of the first echo canceller 16, the third echocanceller 18, and the fourth echo canceller 19 can be set sufficientlysmall compared to a total arithmetic amount in the case where two echocancellers having the same arithmetic amount as the first echo canceller16 are provided to the first microphone 11 and the second microphone 12respectively.

Further, the arrangement positions of the plurality of microphonesdiffer from each other. Accordingly, a waveform of a reflected wave(echo signal) inputted as an acoustic echo differs between the pluralityof microphones. In the case where a phase of an echo signal is oppositeto a phase of an input signal which is a voice of a talker, when theecho signal is added to the input signal, the input signal iseliminated. Accordingly, it is difficult to cancel an acoustic echo ofthe input signal. However, in the first embodiment, a first input signaland a second input signal from at least two microphones are added andhence, an effect of loss of a signal caused by interference of acousticechoes can be reduced.

In the first embodiment, a reproduced signal in a time domain and anaddition signal in a time domain are inputted to the first echocanceller 16, and a first input signal in a time domain, a second inputsignal in the time domain, and a first pseudo echo signal in the timedomain are inputted to the second echo canceller 17. However, thisdisclosure is not particularly limited to such a case. A reproducedsignal in a frequency domain and an addition signal in the frequencydomain may be inputted to the first echo canceller 16, and a first inputsignal in the frequency domain, a second input signal in the frequencydomain, and a first pseudo echo signal in the frequency domain may beinputted to the second echo canceller 17. Hereinafter, a modification 1of the first embodiment is described.

FIG. 3 is a view showing the configuration of a conversation deviceaccording to the modification 1 of the first embodiment of thisdisclosure.

The conversation device shown in FIG. 3 includes an acoustic echocancellation device 1A, a first microphone 11, a second microphone 12,an input terminal 14, a speaker 15, a first output terminal 20, and asecond output terminal 21. In the modification 1 of the firstembodiment, constitutional elements equal to the correspondingconstitutional elements of the first embodiment are given the samesymbols, and the description of these constitutional elements isomitted.

The acoustic echo cancellation device 1A includes an adder 13, a firstecho canceller 16, a second echo canceller 17, fast Fourier transformparts 24, 25, 28, 29, and inverse fast Fourier transform parts 30, 31.

The fast Fourier transform parts 24, 25, 28, 29 perform a discreteFourier transform at a high speed. The fast Fourier transform part 24transforms a reproduced signal in a time domain inputted to the firstecho canceller 16 into a reproduced signal in a frequency domain. Thefast Fourier transform part 25 transforms an addition signal (inputsignal) in a time domain inputted from the adder 13 to the first echocanceller 16 into an addition signal (input signal) in a frequencydomain.

The fast Fourier transform part 28 coverts a first input signal (atleast one input signal) in a time domain inputted from the firstmicrophone 11 to a third echo canceller 18 into a first input signal (atleast one input signal) in a frequency domain. The fast Fouriertransform part 29 transforms a second input signal (at least one inputsignal) in a time domain inputted from the second microphone 12 to afourth echo canceller 19 into a second input signal (at least one inputsignal) in a frequency domain.

The inverse fast Fourier transform parts 30, 31 perform an inversediscrete Fourier transform at a high speed. The inverse fast Fouriertransform part 30 transforms a first input signal in a frequency domaininputted from the third echo canceller 18 to the first output terminal20 into a first input signal in a time domain. The inverse fast Fouriertransform part 31 transforms a second input signal in a frequency domaininputted from the fourth echo canceller 19 to the second output terminal21 into a second input signal in a time domain.

The first echo canceller 16 produces a first pseudo echo signal in afrequency domain using an addition signal in a frequency domain and areproduced signal in a frequency domain.

The third echo canceller 18 produces a third pseudo echo signal in afrequency domain using a first input signal in a frequency domain and afirst pseudo echo signal in a frequency domain, and cancels an acousticecho component of the first input signal in a frequency domain using theproduced third pseudo echo signal in the frequency domain.

The fourth echo canceller 19 produces a fourth pseudo echo signal in afrequency domain using a second input signal in a frequency domain and afirst pseudo echo signal in a frequency domain, and cancels an acousticecho component of the second input signal in the frequency domain usingthe produced fourth pseudo echo signal in the frequency domain.

In the modification 1 of the first embodiment, adaptive filters 161,181, 191 can use an adaptive algorithm in a frequency domain, and aconvolution operation can be performed by multiplication and hence, anarithmetic amount can be further reduced.

In the first embodiment, depending on the arrangement position of thefirst microphone 11, there is a concern that a time difference occursbetween a first input signal from the first microphone 11 and a firstpseudo echo signal produced by the first echo canceller 16. For example,in the case where a sound from a speaker 15 is inputted to the firstmicrophone 11, there is a concern that a first input signal from thefirst microphone 11 contains an echo signal faster in time than a firstpseudo echo signal produced by the first echo canceller 16. In thiscase, theoretically, there is a concern that the third echo canceller 18cannot estimate the echo signal contained in the first input signalusing the first pseudo echo signal. In view of the above, the acousticecho cancellation device may further include a delay part which delaysat least one input signal outputted from at least two microphones.Hereinafter, a modification 2 of the first embodiment is described.

FIG. 10 is a view showing the configuration of a conversation deviceaccording to a modification 2 of the first embodiment of thisdisclosure.

The conversation device shown in FIG. 10 includes an acoustic echocancellation device 1F, a first microphone 11, a second microphone 12,an input terminal 14, a speaker 15, a first output terminal 20, and asecond output terminal 21. In the modification 2 of the firstembodiment, constitutional elements equal to the correspondingconstitutional elements of the first embodiment are given the samesymbols, and the description of these constitutional elements isomitted.

The acoustic echo cancellation device 1F includes an adder 13, a firstecho canceller 16, a second echo canceller 17, and a delay part 80.

The delay part 80 delays at least one input signal outputted from atleast two microphones. The delay part 80 includes a first delay part 81and a second delay part 82.

The first delay part 81 is disposed between the first microphone 11 anda third echo canceller 18. The first delay part 81 delays a first inputsignal from the first microphone 11.

The second delay part 82 is disposed between the second microphone 12and a fourth echo canceller 19. The second delay part 82 delays a secondinput signal from the second microphone 12.

The second echo canceller 17 produces a second pseudo echo signal whichindicates a component of a first pseudo echo signal contained in atleast one delayed input signal using at least one delayed input signaland the first pseudo echo signal produced by the first echo canceller16, and cancels an acoustic echo component of at least one delayed inputsignal using the produced second pseudo echo signal.

The third echo canceller 18 produces a third pseudo echo signal whichindicates a component of a first pseudo echo signal contained in adelayed first input signal using the delayed first input signal and thefirst pseudo echo signal produced by the first echo canceller 16, andcancels an acoustic echo component of the delayed first input signalusing the produced third pseudo echo signal.

The fourth echo canceller 19 produces a fourth pseudo echo signal whichindicates a component of a first pseudo echo signal contained in adelayed second input signal using the delayed second input signal andthe first pseudo echo signal produced by the first echo canceller 16,and cancels an acoustic echo component of the delayed second inputsignal using the produced fourth pseudo echo signal.

In the modification 2 of the first embodiment, a first input signaldelayed by the first delay part 81 is inputted to the third echocanceller 18, and a second input signal delayed by the second delay part82 is inputted to the fourth echo canceller 19. Accordingly, a timedifference between the first pseudo echo signal produced by the firstecho canceller 16 and the first input signal is eliminated, and a timedifference between the first pseudo echo signal and the second inputsignal is eliminated and hence, it is possible to produce a third pseudoecho signal and a fourth pseudo echo signal with certainty.

In the modification 1 of the first embodiment, the acoustic echocancellation device 1A may include the first delay part 81 between thefirst microphone 11 and the fast Fourier transform part 28, and mayinclude the second delay part 82 between the second microphone 12 andthe fast Fourier transform part 29.

In the first embodiment, the adder 13 adds a first input signal from thefirst microphone 11 and a second input signal from the second microphone12 to each other, and the first echo canceller 16 produces a firstpseudo echo signal which indicates a component of a reproduced signalcontained in an addition signal using the addition signal and thereproduced signal. However, this disclosure is not particularly limitedto such a case, and the acoustic echo cancellation device 1 may furtherinclude an averaging processing part which averages the addition signalfrom the adder 13. In this case, the first echo canceller 16 may producea first pseudo echo signal which indicates a component of a reproducedsignal contained in an averaging signal using the averaging signal fromthe averaging processing part and the reproduced signal.

Second Embodiment

In the first embodiment, a first pseudo echo signal produced by thefirst echo canceller is outputted to the third echo canceller and thefourth echo canceller, the third echo canceller cancels an acoustic echocomponent of a first input signal using the first pseudo echo signal,and the fourth echo canceller cancels an acoustic echo component of asecond input signal using the first pseudo echo signal. On the otherhand, in the second embodiment, the first echo canceller produces afirst pseudo echo signal, cancels an acoustic echo component of a firstinput signal using the first pseudo echo signal, and the second echocanceller cancels an acoustic echo component of a second input signalusing the first pseudo echo signal.

FIG. 4 is a view showing the configuration of a conversation deviceaccording to the second embodiment of this disclosure.

The conversation device shown in FIG. 4 includes an acoustic echocancellation device 1B, a first microphone 11, a second microphone 12,an input terminal 14, a speaker 15, a first output terminal 20, and asecond output terminal 21. In the second embodiment, constitutionalelements equal to the corresponding constitutional elements of the firstembodiment are given the same symbols, and the description of theseconstitutional elements is omitted.

The acoustic echo cancellation device 1B includes a first echo canceller41 and a second echo canceller 42.

The first echo canceller 41 produces a first pseudo echo signal whichindicates a component of a reproduced signal contained in an inputsignal using an input signal obtained from at least two microphones anda reproduced signal outputted to the speaker.

It is preferable that the first echo canceller 41 produce a first pseudoecho signal with respect to the microphone disposed at the positionclosest to the speaker 15. In this case, the first echo canceller 41produces a first pseudo echo signal which indicates a component of areproduced signal contained in an input signal using the input signaloutputted from the microphone disposed at the position closest to thespeaker 15 and the reproduced signal. In the second embodiment, themicrophone disposed at the position closest to the speaker 15 is thefirst microphone 11.

In the second embodiment, an input signal obtained from at least twomicrophones is a first input signal from the first microphone 11. Thatis, the first echo canceller 41 produces a first pseudo echo signalwhich indicates a component of a reproduced signal contained in thefirst input signal using the first input signal and the reproducedsignal. Further, the first echo canceller 41 cancels an acoustic echocomponent of the first input signal using the produced first pseudo echosignal.

The first echo canceller 41 includes an adaptive filter 411 and an errorcalculation part 412. The adaptive filter 411 produces a first pseudoecho signal which indicates a component of a reproduced signal containedin a first input signal by convoluting a filter coefficient and thereproduced signal.

The error calculation part 412 calculates an error signal between thefirst input signal from the first microphone 11 and the first pseudoecho signal from the adaptive filter 411, and outputs a calculated errorsignal to the adaptive filter 411. The adaptive filter 411 modifies afilter coefficient based on an inputted error signal, and produces afirst pseudo echo signal by convoluting a modified filter coefficientand a reproduced signal. The adaptive filter 411 modifies the filtercoefficient such that the error signal is minimized using an adaptivealgorithm. As the adaptive algorithm, for example, an NLMS method, an APmethod, or an RLS method can be used.

The error calculation part 412 cancels an acoustic echo component from afirst input signal by subtracting a first pseudo echo signal from theadaptive filter 411 from a first input signal from the first microphone11. Accordingly, the error calculation part 412 outputs a first inputsignal in which an acoustic echo component is cancelled to the firstoutput terminal 20.

A first pseudo echo signal produced by the first echo canceller 41 isoutputted to the second echo canceller 42.

The second echo canceller 42 produces a second pseudo echo signal whichindicates a component of a first pseudo echo signal contained in asecond input signal using a second input signal and a first pseudo echosignal produced by the first echo canceller 41, and cancels an acousticecho component of a second input signal using a produced second pseudoecho signal.

The second echo canceller 42 includes an adaptive filter 421 and anerror calculation part 422.

The adaptive filter 421 produces a second pseudo echo signal whichindicates a component of the first pseudo echo signal contained in thesecond input signal by convoluting a filter coefficient and the firstpseudo echo signal.

The error calculation part 422 calculates an error signal between asecond input signal from a second microphone 12 and the second pseudoecho signal from the adaptive filter 421, and outputs the calculatederror signal to the adaptive filter 421. The adaptive filter 421modifies a filter coefficient based on an inputted error signal, andproduces a second pseudo echo signal by convoluting a modified filtercoefficient and a first pseudo echo signal. The adaptive filter 421modifies a filter coefficient such that an error signal is minimizedusing an adaptive algorithm. As the adaptive algorithm, for example, anNLMS method, an AP method, or an RLS method can be used.

The error calculation part 422 cancels an acoustic echo component from asecond input signal by subtracting a second pseudo echo signal from theadaptive filter 421 from a second input signal from the secondmicrophone 12. Accordingly, the error calculation part 422 outputs asecond input signal in which an acoustic echo component is cancelled tothe second output terminal 21.

In the second embodiment, the conversation device includes twomicrophones. However, this disclosure is not particularly limited tosuch a case, and the conversation device may include three or moremicrophones. When the conversation device includes three or moremicrophones, the first echo canceller 41 outputs a first pseudo echosignal to echo cancellers which are provided to the respectivemicrophones other than the first microphone 11.

In the second embodiment, the conversation device includes one speaker.However, this disclosure is not particularly limited to such a case, andthe conversation device may include two or more speakers. In the casewhere the conversation device includes a plurality of speakers, it isnecessary for the conversation device to include the same number ofacoustic echo cancellation devices 1B as the plurality of speakers.

Next, an operation of the acoustic echo cancellation device 1B accordingto the second embodiment of this disclosure is described.

FIG. 5 is a flowchart for describing an operation of the acoustic echocancellation device according to the second embodiment of thisdisclosure.

First, in step S21, the adaptive filter 411 of the first echo canceller41 produces a first pseudo echo signal which indicates a component of areproduced signal contained in a first input signal by convoluting afilter coefficient and the reproduced signal.

Next, in step S22, the error calculation part 412 calculates an errorsignal between a first input signal from the first microphone 11 and afirst pseudo echo signal from the adaptive filter 411 by subtracting thefirst pseudo echo signal from the first input signal. The errorcalculation part 412 outputs the calculated error signal to the adaptivefilter 411.

Next, in step S23, the adaptive filter 411 modifies a filter coefficientbased on an error signal inputted from the error calculation part 412.The adaptive filter 411 produces a first pseudo echo signal byconvoluting a modified filter coefficient and a reproduced signal.

Next, in step S24, the error calculation part 412 outputs a first inputsignal in which an acoustic echo component is cancelled to the firstoutput terminal 20. That is, the error calculation part 412 cancels anacoustic echo component from a first input signal by subtracting a firstpseudo echo signal from the adaptive filter 411 from a first inputsignal from the first microphone 11.

Next, in step S25, the adaptive filter 411 outputs a produced firstpseudo echo signal to a second echo canceller 42.

Next, in step S26, the adaptive filter 421 of the second echo canceller42 produces a second pseudo echo signal which indicates a component ofthe first pseudo echo signal contained in the second input signal byconvoluting a filter coefficient and a first pseudo echo signal.

Next, in step S27, the error calculation part 422 calculates an errorsignal between a second input signal from the second microphone 12 and asecond pseudo echo signal from the adaptive filter 421 by subtractingthe second pseudo echo signal from the second input signal. The errorcalculation part 422 outputs the calculated error signal to the adaptivefilter 421.

Next, in step S28, the adaptive filter 421 modifies a filter coefficientbased on the error signal inputted from the error calculation part 422.The adaptive filter 421 produces the second pseudo echo signal byconvoluting the modified filter coefficient and the first pseudo echosignal.

Next, in step S29, the error calculation part 422 outputs the secondinput signal in which the acoustic echo component is cancelled to thesecond output terminal 21. That is, the error calculation part 422cancels an acoustic echo component from the second input signal bysubtracting the second pseudo echo signal from the adaptive filter 421from the second input signal from the second microphone 12.

In an initial stage where the acoustic echo cancellation device 1Bstarts its operation, the filter coefficient is not sufficientlymodified. Accordingly, an acoustic echo component cannot be sufficientlycancelled from the first input signal and the second input signal.However, by repeatedly performing processing in step S21 to step S29,the filter coefficient is sufficiently modified and hence, the acousticecho component can be sufficiently cancelled from the first input signaland the second input signal.

In this manner, the first echo canceller 41 produces the first pseudoecho signal which indicates a component of the reproduced signalcontained in the first input signal obtained from the first microphone11, and cancels the acoustic echo component of the first input signalusing the produced first pseudo echo signal, and the second echocanceller 42 produces a second pseudo echo signal which indicates acomponent of the first pseudo echo signal contained in the second inputsignal, and cancels an acoustic echo component of the second inputsignal using the produced second pseudo echo signal.

Accordingly, the second pseudo echo signal is produced using the alreadyproduced first pseudo echo signal. Accordingly, a filter length (taplength) of the adaptive filter used in producing the second pseudo echosignal can be shortened and hence, a conversation performance can bemaintained and, at the same time, an arithmetic amount for removing anacoustic echo can be reduced.

Particularly, echo cancelling processing by the echo canceller on afirst stage (first echo canceller 41) has substantially the same filterlength (arithmetic amount) compared to the prior art. However, echocancelling processing by the echo cancellers on the second stage andsucceeding stages (second echo canceller 42) uses the already producedfirst pseudo echo signal and hence, can have a short filter lengthcompared to the prior art. As a result, an arithmetic amount can bereduced compared to the prior art. Accordingly, the larger the number ofmicrophone becomes, the smaller an arithmetic amount becomes compared tothe prior art.

In the second embodiment, the first echo canceller 41 produces a firstpseudo echo signal using a first input signal from the first microphone11 and the reproduced signal transmitted to the speaker 15. In thiscase, it is considered that an acoustic echo inputted to the firstmicrophone 11 from the speaker 15 is estimated. The second echocanceller 42 produces a second pseudo echo signal using a first pseudoecho signal produced by the first echo canceller 16. In this case, it isconsidered that an acoustic echo corresponding to a differential betweenthe position of the first microphone 11 and the position of the secondmicrophone 12 is estimated. Accordingly, a filter length of the adaptivefilter 421 of the second echo canceller 42 can be set largely shorterthan a filter length of the adaptive filter 411 of the first echocanceller 41.

For example, an arithmetic amount of the second echo canceller 42 can bereduced to approximately one tenth of an arithmetic amount of the firstecho canceller 41. Accordingly, a total arithmetic amount of the firstecho canceller 41 and the second echo canceller 42 can be setsufficiently small compared to a total arithmetic amount in the casewhere two echo cancellers having the same arithmetic amount as the firstecho canceller 41 are provided to the first microphone 11 and the secondmicrophone 12 respectively.

In the second embodiment, the acoustic echo cancellation device 1B mayinclude a delay part between the second microphone 12 and the secondecho canceller 42.

In the second embodiment, a reproduced signal in a time domain and afirst input signal in a time domain are inputted to the first echocanceller 41, and a second input signal in the time domain and a firstpseudo echo signal in the time domain are inputted to the second echocanceller 42. However, this disclosure is not particularly limited tosuch a case. A reproduced signal in a frequency domain and a first inputsignal in a frequency domain may be inputted to the first echo canceller41, and a second input signal in a frequency domain and a first pseudoecho signal in a frequency domain may be inputted to the second echocanceller 42. Hereinafter, a modification of the second embodiment isdescribed.

FIG. 6 is a view showing the configuration of a conversation deviceaccording to a modification of the second embodiment of this disclosure.

The conversation device shown in FIG. 6 includes an acoustic echocancellation device 1C, a first microphone 11, a second microphone 12,an input terminal 14, a speaker 15, a first output terminal 20, and asecond output terminal 21. In the modification of the second embodiment,constitutional elements equal to the corresponding constitutionalelements of the second embodiment are given the same symbols, and thedescription of these constitutional elements is omitted.

The acoustic echo cancellation device 1C includes a first echo canceller41, a second echo canceller 42, fast Fourier transform parts 45, 46, 49,and inverse fast Fourier transform parts 50, 51.

The fast Fourier transform parts 45, 46, 49 perform a discrete Fouriertransform at a high speed. The fast Fourier transform part 45 transformsa reproduced signal in a time domain inputted to the first echocanceller 41 into a reproduced signal in a frequency domain. The fastFourier transform part 46 transforms a first input signal in a timedomain inputted from the first microphone 11 to the first echo canceller41 into a first input signal in a frequency domain. The fast Fouriertransform part 49 transforms a second input signal in a time domaininputted from the second microphone 12 to the second echo canceller 42into a second input signal in a frequency domain.

The inverse fast Fourier transform parts 50, 51 perform an inversediscrete Fourier transform at a high speed. The inverse fast Fouriertransform part 50 transforms a first input signal in a frequency domaininputted from the first echo canceller 41 to the first output terminal20 into a first input signal in a time domain. The inverse fast Fouriertransform part 51 transforms a second input signal in a frequency domaininputted from the second echo canceller 42 to the second output terminal21 into a second input signal in a time domain.

The first echo canceller 41 produces a first pseudo echo signal in afrequency domain using a first input signal in a frequency domain and areproduced signal in a frequency domain, and cancels an acoustic echocomponent of the first input signal in a frequency domain using theproduced first pseudo echo signal in a frequency domain.

The second echo canceller 42 produces a second pseudo echo signal in afrequency domain using the second input signal in a frequency domain andthe first pseudo echo signal in a frequency domain, and cancels anacoustic echo component of the second input signal in a frequency domainusing the produced second pseudo echo signal in a frequency domain.

In the modification of the second embodiment, adaptive filters 411, 421can use an adaptive algorithm in a frequency domain, and a convolutionoperation can be performed by multiplication and hence, an arithmeticamount can be further reduced.

In the modification of the second embodiment, the acoustic echocancellation device 1C may include a delay part between the secondmicrophone 12 and the fast Fourier transform part 49.

Third Embodiment

In the first embodiment, the first echo canceller produces a firstpseudo echo signal which indicates a component of a reproduced signalcontained in an addition signal using the addition signal from the adderand the reproduced signal. On the other hand, in the third embodiment,the first echo canceller calculates a first error signal which indicatesan error between a first input signal and a first pseudo echo signal,calculates a second error signal which indicates an error between asecond input signal and a first pseudo echo signal, averages an additionsignal obtained by adding the first error signal and the second errorsignal to each other, and produces the first pseudo echo signal whichindicates a component of a reproduced signal contained in the averagesignal using the average signal and the reproduced signal.

FIG. 7 is a view showing the configuration of a conversation deviceaccording to the third embodiment of this disclosure.

The conversation device shown in FIG. 7 includes an acoustic echocancellation device 1D, a first microphone 11, a second microphone 12,an input terminal 14, a speaker 15, a first output terminal 20, and asecond output terminal 21. In the third embodiment, constitutionalelements equal to the corresponding constitutional elements of the firstembodiment are given the same symbols, and the description of theseconstitutional elements is omitted.

The acoustic echo cancellation device 1D includes a first echo canceller61, and a second echo canceller 17.

The first echo canceller 61 produces a first pseudo echo signal whichindicates a component of the reproduced signal contained in the inputsignal using an input signal obtained from at least two microphones anda reproduced signal outputted to the speaker.

In the third embodiment, an input signal obtained from at least twomicrophones is an average signal obtained by averaging an additionsignal which is obtained by adding a first error signal which indicatesan error between a first input signal and a first pseudo echo signal anda second error signal which indicates an error between a second inputsignal and the first pseudo echo signal to each other. That is, thefirst echo canceller 61 produces a first pseudo echo signal whichindicates a component of a reproduced signal contained in an averagesignal using an average signal and the reproduced signal.

The first echo canceller 61 includes an adaptive filter 611, a firsterror calculation part 612, a second error calculation part 613, and anaveraging processing part 614.

The adaptive filter 611 produces a first pseudo echo signal whichindicates a component of a reproduced signal contained in an averagesignal by convoluting a filter coefficient and the reproduced signal.

The first error calculation part 612 calculates a first error signalwhich indicates an error between a first input signal and a first pseudoecho signal. The first error calculation part 612 outputs the calculatedfirst error signal to the second error calculation part 613.

The second error calculation part 613 calculates a second error signalwhich indicates an error between a second input signal and a firstpseudo echo signal, and adds the first error signal and the second errorsignal to each other. The second error calculation part 613 outputs anaddition signal obtained by adding a first error signal and a seconderror signal to each other to the averaging processing part 614.

The averaging processing part 614 averages the addition signal obtainedby adding the first error signal and the second error signal to eachother. The averaging processing part 614 outputs an average signalobtained by averaging an addition signal which is obtained by adding afirst error signal and a second error signal to each other to theadaptive filter 611.

The adaptive filter 611 produces a first pseudo echo signal whichindicates a component of a reproduced signal contained in an averagesignal using an average signal from the averaging processing part 614and a reproduced signal. The adaptive filter 611 modifies a filtercoefficient based on an inputted average signal, and produces a firstpseudo echo signal by convoluting a modified filter coefficient and areproduced signal. The adaptive filter 611 modifies a filter coefficientsuch that an average signal is minimized using an adaptive algorithm. Asthe adaptive algorithm, for example, an NLMS method, an AP method, or anRLS method can be used.

A first pseudo echo signal produced by the first echo canceller 61 isoutputted to the third echo canceller 18 and the fourth echo canceller19.

In the third embodiment, the conversation device includes twomicrophones. However, this disclosure is not particularly limited tosuch a case, and the conversation device may include three or moremicrophones. When the conversation device includes three or moremicrophones, the first echo canceller 61 performs adding and averagingof error signals between respective input signals from three or moremicrophones and a first pseudo echo signal, and outputs the first pseudoecho signal to echo cancellers which are provided to the respectivethree or more microphones.

In the third embodiment, the conversation device includes one speaker.However, this disclosure is not particularly limited to such a case, andthe conversation device may include two or more speakers. In the casewhere the conversation device includes a plurality of speakers, it isnecessary for the conversation device to include the same number ofacoustic echo cancellation devices 1D as the plurality of speakers.

Next, an operation of the acoustic echo cancellation device 1D accordingto the third embodiment of this disclosure is described.

FIG. 8 is a flowchart for describing an operation of the acoustic echocancellation device according to the third embodiment of thisdisclosure.

First, in step S41, the adaptive filter 611 of the first echo canceller61 produces a first pseudo echo signal which indicates a component of areproduced signal contained in an average signal by convoluting a filtercoefficient and the reproduced signal.

Next, in step S42, the first error calculation part 612 calculates afirst error signal which is a differential between the first inputsignal from the first microphone 11 and the first pseudo echo signalfrom the adaptive filter 611 by subtracting the first pseudo echo signalfrom the first input signal. The first error calculation part 612outputs the calculated first error signal to the second errorcalculation part 613.

Next, in step S43, the second error calculation part 613 calculates asecond error signal which is a differential between the second inputsignal from the second microphone 12 and the first pseudo echo signalfrom the adaptive filter 611 by subtracting the first pseudo echo signalfrom the second input signal.

Next, in step S44, the second error calculation part 613 adds the firsterror signal and the second error signal. The second error calculationpart 613 outputs a calculated addition signal obtained by adding thefirst error signal and the second error signal to each other to theaveraging processing part 614.

Next, in step S45, the averaging processing part 614 averages theaddition signal obtained by adding the first error signal and the seconderror signal to each other. The averaging processing part 614 outputs anaverage signal obtained by averaging the addition signal to the adaptivefilter 611.

Next, in step S46, the adaptive filter 611 modifies a filter coefficientbased on the average signal inputted from the averaging processing part614. The adaptive filter 611 produces the first pseudo echo signal byconvoluting the modified filter coefficient and the reproduced signal.

Next, in step S47, the adaptive filter 611 outputs the produced firstpseudo echo signal to the third echo canceller 18 and the fourth echocanceller 19.

Next, in step S48, the adaptive filter 181 of the third echo canceller18 produces a third pseudo echo signal which indicates a component ofthe first pseudo echo signal contained in the first input signal byconvoluting the filter coefficient and the first pseudo echo signal.

Next, in step S49, the error calculation part 182 calculates a thirderror signal between the first input signal from the first microphone 11and the third pseudo echo signal from the adaptive filter 181 bysubtracting the third pseudo echo signal from the first input signal.The error calculation part 182 outputs the calculated third error signalto the adaptive filter 181.

Next, in step S50, the adaptive filter 181 modifies a filter coefficientbased on the third error signal inputted from the error calculation part182. The adaptive filter 181 produces the third pseudo echo signal byconvoluting the modified filter coefficient and the first pseudo echosignal.

Next, in step S51, the error calculation part 182 outputs the firstinput signal in which the acoustic echo component is cancelled to thefirst output terminal 20. That is, the error calculation part 182cancels an acoustic echo component from the first input signal bysubtracting the third pseudo echo signal from the adaptive filter 181from the first input signal from the first microphone 11.

Next, in step S52, the adaptive filter 191 of the fourth echo canceller19 produces a fourth pseudo echo signal which indicates a component ofthe first pseudo echo signal contained in the second input signal byconvoluting the filter coefficient and the first pseudo echo signal.

Next, in step S53, the error calculation part 192 calculates a fourtherror signal between the second input signal from the second microphone12 and the fourth pseudo echo signal from the adaptive filter 191 bysubtracting the fourth pseudo echo signal from the second input signal.The error calculation part 192 outputs the calculated fourth errorsignal to the adaptive filter 191.

Next, in step S54, the adaptive filter 191 modifies a filter coefficientbased on the fourth error signal inputted from the error calculationpart 192. The adaptive filter 191 produces the fourth pseudo echo signalby convoluting the modified filter coefficient and the first pseudo echosignal.

Next, in step S55, the error calculation part 192 outputs the secondinput signal in which the acoustic echo component is cancelled to thesecond output terminal 21. That is, the error calculation part 192cancels an acoustic echo component from the second input signal bysubtracting the fourth pseudo echo signal from the adaptive filter 191from the second input signal from the second microphone 12.

In an initial stage where the acoustic echo cancellation device 1Dstarts its operation, the filter coefficient is not sufficientlymodified. Accordingly, an acoustic echo component cannot be sufficientlycancelled from the first input signal and the second input signal.However, by repeatedly performing processing in step S41 to step S55,the filter coefficient is sufficiently modified and hence, the acousticecho component can be sufficiently cancelled from the first input signaland the second input signal.

In this manner, the first echo canceller 61 produces the first pseudoecho signal which indicates a component of the reproduced signalcontained in the input signals obtained from at least two microphones,and the second echo canceller 17 produces a second pseudo echo signalwhich indicates a component of the first pseudo echo signal contained inat least one input signal, and cancels an acoustic echo component of atleast one input signal using the produced second pseudo echo signal.

Accordingly, the second pseudo echo signal is produced using the alreadyproduced first pseudo echo signal. Accordingly, a filter length (taplength) of the adaptive filter used in producing the second pseudo echosignal can be shortened and hence, a conversation performance can bemaintained and, at the same time, an arithmetic amount for removing anacoustic echo can be reduced.

Particularly, echo cancelling processing by the echo canceller on afirst stage (first echo canceller 61) has substantially the same filterlength (arithmetic amount) compared to the prior art. However, echocancelling processing by the echo cancellers on the second stage andsucceeding stages (the third echo canceller 18 and the fourth echocanceller 19) uses the already produced first pseudo echo signal andhence, can have a short filter length compared to the prior art. As aresult, an arithmetic amount can be reduced compared to the prior art.Accordingly, the larger the number of microphone becomes, the smaller anarithmetic amount becomes compared to the prior art.

Further, the arrangement positions of the plurality of microphonesdiffer from each other. Accordingly, a waveform of a reflected wave(echo signal) inputted as an acoustic echo differs between the pluralityof microphones. In the case where a phase of an echo signal is oppositeto a phase of an input signal which is a voice of a talker, when theecho signal is added to the input signal, the input signal iseliminated. Accordingly, it is difficult to cancel an acoustic echo ofthe input signal. However, in the third embodiment, the respective errorsignals of the first input signal and the second input signal from atleast two microphones are added to each other and are averaged andhence, an effect of loss of a signal caused by interference of acousticechoes can be reduced.

In the third embodiment, the acoustic echo cancellation device 1D mayinclude a first delay part 81 between the first microphone 11 and thethird echo canceller 18, or may include a second delay part 82 betweenthe second microphone 12 and the fourth echo canceller 19.

In the third embodiment, a reproduced signal in a time domain, a firstinput signal in the time domain, and a second input signal in the timedomain are inputted to the first echo canceller 61, and a first inputsignal in a time domain, a second input signal in the time domain, and afirst pseudo echo signal in the time domain are inputted to the secondecho canceller 17. However, this disclosure is not particularly limitedto such a case. A reproduced signal in a frequency domain, a first inputsignal in the frequency domain, and a second input signal in thefrequency domain may be inputted to the first echo canceller 61, and afirst input signal in a frequency domain, a second input signal in thefrequency domain, and a first pseudo echo signal in the frequency domainmay be inputted to the second echo canceller 17. Hereinafter, amodification of the third embodiment is described.

FIG. 9 is a view showing the configuration of a conversation deviceaccording to a modification of the third embodiment of this disclosure.

The conversation device shown in FIG. 9 includes an acoustic echocancellation device 1E, a first microphone 11, a second microphone 12,an input terminal 14, a speaker 15, a first output terminal 20, and asecond output terminal 21. In the modification of the third embodiment,constitutional elements equal to the corresponding constitutionalelements of the third embodiment are given the same symbols, and thedescription of these constitutional elements is omitted.

The acoustic echo cancellation device 1E includes a first echo canceller61, a second echo canceller 17, fast Fourier transform parts 64, 65, 66,and inverse fast Fourier transform parts 69, 70.

The fast Fourier transform parts 64, 65, 66 perform a discrete Fouriertransform at a high speed. The fast Fourier transform part 64 transformsa reproduced signal in a time domain inputted to the first echocanceller 61 into a reproduced signal in a frequency domain. The fastFourier transform part 65 transforms a first input signal in a timedomain outputted from the first microphone 11 into a first input signalin a frequency domain. The fast Fourier transform part 66 transforms asecond input signal in a time domain outputted from the secondmicrophone 12 into a second input signal in a frequency domain.

The inverse fast Fourier transform parts 69, 70 perform an inversediscrete Fourier transform at a high speed. The inverse fast Fouriertransform part 69 transforms a first input signal in a frequency domaininputted from the third echo canceller 18 to the first output terminal20 into a first input signal in a time domain. The inverse fast Fouriertransform part 70 transforms a second input signal in a frequency domaininputted from the fourth echo canceller 19 to the second output terminal21 into a second input signal in a time domain.

The first echo canceller 61 produces a first pseudo echo signal in afrequency domain using a first input signal in a frequency domain, and asecond input signal in a frequency domain, and a reproduced signal in afrequency domain.

The third echo canceller 18 produces a third pseudo echo signal in afrequency domain using a first input signal in a frequency domain and afirst pseudo echo signal in a frequency domain, and cancels an acousticecho component of the first input signal in a frequency domain using theproduced third pseudo echo signal in the frequency domain.

The fourth echo canceller 19 produces a fourth pseudo echo signal in afrequency domain using a second input signal in a frequency domain and afirst pseudo echo signal in a frequency domain, and cancels an acousticecho component of the second input signal in the frequency domain usingthe produced fourth pseudo echo signal in the frequency domain.

In the modification of the third embodiment, adaptive filters 611, 181,191 can use an adaptive algorithm in a frequency domain, and aconvolution operation can be performed by multiplication and hence, anarithmetic amount can be further reduced.

In the modification of the third embodiment, the acoustic echocancellation device 1E may include the first delay part 81 between thefirst microphone 11 and the third echo canceller 18, and may include thesecond delay part 82 between the second microphone 12 and the fourthecho canceller 19. In this case, the fast Fourier transform part 65 isdisposed between a branch point between the first microphone 11 and theerror calculation part 182 and the first error calculation part 612, andthe first delay part 81 and the fast Fourier transform part are disposedbetween the branch point and the error calculation part 182. The fastFourier transform part 66 is disposed between a branch point between thesecond microphone 12 and the error calculation part 192 and the seconderror calculation part 613, and the second delay part 82 and the fastFourier transform part are disposed between the branch point and theerror calculation part 192.

In the above-mentioned respective embodiments, each constitutionalelement may be formed of a dedicated hardware, or may be realized byexecuting a software program suitable for each constitutional element.Each constitutional element may be realized by allowing a programexecuting part such as a CPU or a processor to read a software programrecorded in a recording medium such as a hard disc or a semiconductormemory and to execute the software program.

A part or the entirety of functions of the device according to theembodiment of this disclosure is typically realized in the form of largescale integration (LSI) which is an integrated circuit. Theseconstitutional parts may be individually formed as one chip or may beformed as one chip such that one chip includes some of or allconstitutional elements. The integrated circuit is not limited to LSI,and may be realized in the form of a dedicated circuit or ageneral-purpose processor. It is also possible to use a FieldProgrammable Gate Array (FPGA) which is programmable after manufacturingan LSI or a reconfigurable processor capable of reconstructing theconnection and the setting of circuit cells in an LSI.

A part of or the entirety of functions of the device according to theembodiment of this disclosure may be realized by allowing a processorsuch as a CPU to execute a program.

Numerals used in the description made heretofore are exemplified forspecifically describing this disclosure, and this disclosure is notlimited to the exemplified numerals.

The order that the respective steps indicated in the previouslydescribed flowchart are exemplified for specifically describing thisdisclosure, and the steps may be performed in the orders other than theabove-mentioned order within the scope that substantially the sameadvantageous effects of the present invention can be acquired. A part ofthe above-mentioned step may be performed simultaneously with (parallelwith) other steps.

The acoustic echo cancellation device, the acoustic echo cancellationmethod and the non-transitory computer readable recording mediumrecording an acoustic echo cancellation program according to thisdisclosure can maintain a conversation performance and can reduce anarithmetic amount for removing an acoustic echo. Accordingly, theacoustic echo cancellation device, the acoustic echo cancellation methodand the non-transitory computer readable recording medium recording anacoustic echo cancellation program are useful as an acoustic echocancellation device, an acoustic echo cancellation method, and anon-transitory computer readable recording medium recording an acousticecho cancellation program which cancel an acoustic echo component of aninput signal outputted from a microphone.

This application is based on U.S. Provisional Application No. 62/778,684filed in the United States Patent and Trademark Office on Dec. 12, 2018,Japanese Patent application No. 2019-073738 filed in Japan Patent Officeon Apr. 8, 2019, and Japanese Patent application No. 2019-163681 filedin Japan Patent Office on Sep. 9, 2019, the contents of which are herebyincorporated by reference.

Although the present invention has been fully described by way ofexample with reference to the accompanying drawings, it is to beunderstood that various changes and modifications will be apparent tothose skilled in the art. Therefore, unless otherwise such changes andmodifications depart from the scope of the present invention hereinafterdefined, they should be construed as being included therein.

1. An acoustic echo cancellation device comprising: a first echocanceller which, using an input signal obtained from at least twomicrophones and a reproduced signal outputted to a speaker, produces afirst pseudo echo signal which indicates a component of the reproducedsignal contained in the input signal; and a second echo canceller which,using at least one input signal outputted from the at least twomicrophones and the first pseudo echo signal produced by the first echocanceller, produces a second pseudo echo signal which indicates acomponent of the first pseudo echo signal contained in the at least oneinput signal, and cancels an acoustic echo component of the at least oneinput signal using the produced second pseudo echo signal.
 2. Theacoustic echo cancellation device according to claim 1, furthercomprising a delay part which delays at least one input signal outputtedfrom the at least two microphones, wherein the second echo cancellerproduces a second pseudo echo signal which indicates a component of thefirst pseudo echo signal contained in the at least one delayed inputsignal using the at least one delayed input signal and the first pseudoecho signal produced by the first echo canceller, and cancels anacoustic echo component of the at least one delayed input signal usingthe produced second pseudo echo signal.
 3. The acoustic echocancellation device according to claim 2, wherein the at least twomicrophones includes a first microphone which outputs a first inputsignal, and a second microphone which outputs a second input signal, thedelay part includes a first delay part which delays the first inputsignal and a second delay part which delays the second input signal, theacoustic echo cancellation device further includes an adder which addsthe first input signal and the second input signal to each other, thefirst echo canceller produces the first pseudo echo signal whichindicates a component of the reproduced signal contained in an additionsignal using the addition signal from the adder and the reproducedsignal, the second echo canceller includes: a third echo canceller whichproduces a third pseudo echo signal which indicates a component of thefirst pseudo echo signal contained in the delayed first input signalusing the delayed first input signal and the first pseudo echo signalproduced by the first echo canceller, and cancels an acoustic echocomponent of the delayed first input signal using the produced thirdpseudo echo signal; and a fourth echo canceller which produces a fourthpseudo echo signal which indicates a component of the first pseudo echosignal contained in the delayed second input signal using the delayedsecond input signal and the first pseudo echo signal produced by thefirst echo canceller, and cancels an acoustic echo component of thedelayed second input signal using the produced fourth pseudo echosignal.
 4. The acoustic echo cancellation device according to claim 1,wherein the at least two microphones include a first microphone whichoutputs a first input signal, and a second microphone which outputs asecond input signal, the acoustic echo cancellation device furtherincludes an adder which adds the first input signal and the second inputsignal to each other, the first echo canceller produces the first pseudoecho signal which indicates a component of the reproduced signalcontained in an addition signal using the addition signal from the adderand the reproduced signal, the second echo canceller includes: a thirdecho canceller which produces a third pseudo echo signal which indicatesa component of the first pseudo echo signal contained in the first inputsignal using the first input signal and the first pseudo echo signalproduced by the first echo canceller, and cancels an acoustic echocomponent of the first input signal using the produced third pseudo echosignal; and a fourth echo canceller which produces a fourth pseudo echosignal which indicates a component of the first pseudo echo signalcontained in the second input signal using the second input signal andthe first pseudo echo signal produced by the first echo canceller, andcancels an acoustic echo component of the second input signal using theproduced fourth pseudo echo signal.
 5. The acoustic echo cancellationdevice according to claim 1, wherein the at least two microphonesinclude a first microphone which outputs a first input signal, and asecond microphone which outputs a second input signal, the first echocanceller produces the first pseudo echo signal which indicates acomponent of the reproduced signal contained in the first input signalusing the first input signal and the reproduced signal, and cancels anacoustic echo component of the first input signal using the producedfirst pseudo echo signal, and the second echo canceller produces asecond pseudo echo signal which indicates a component of the firstpseudo echo signal contained in the second input signal using the secondinput signal and the first pseudo echo signal produced by the first echocanceller, and cancels an acoustic echo component of the second inputsignal using the produced second pseudo echo signal.
 6. The acousticecho cancellation device according to claim 1, wherein the at least twomicrophones includes a first microphone which outputs a first inputsignal, and a second microphone which outputs a second input signal, thefirst echo canceller includes: a first calculation part that calculatesa first error signal which indicates an error between the first inputsignal and the first pseudo echo signal; a second calculation part thatcalculates a second error signal which indicates an error between thesecond input signal and the first pseudo echo signal; an averagingprocessing part that averages an addition signal obtained by adding thefirst error signal and the second error signal to each other; and aproducing part that produces the first pseudo echo signal whichindicates a component of the reproduced signal contained in an averagesignal using the average signal from the averaging processing part andthe reproduced signal, and the second echo canceller includes: a thirdecho canceller which produces a third pseudo echo signal which indicatesa component of the first pseudo echo signal contained in the first inputsignal using the first input signal and the first pseudo echo signalproduced by the first echo canceller, and cancels an acoustic echocomponent of the first input signal using the produced third pseudo echosignal; and a fourth echo canceller which produces a fourth pseudo echosignal which indicates a component of the first pseudo echo signalcontained in the second input signal using the second input signal andthe first pseudo echo signal produced by the first echo canceller, andcancels an acoustic echo component of the second input signal using theproduced fourth pseudo echo signal.
 7. The acoustic echo cancellationdevice according to claim 1, further comprising: a first converting partthat converts the input signal in a time domain into an input signal ina frequency domain; a second converting part that converts thereproduced signal in a time domain into a reproduced signal in afrequency domain; a third converting part that converts the at least oneinput signal in a time domain into at least one input signal in afrequency domain; and a fourth converting part that converts the firstpseudo echo signal in a time domain into a first pseudo echo signal in afrequency domain.
 8. The acoustic echo cancellation device according toclaim 1, wherein a filter length of the second echo canceller is shorterthan a filter length of the first echo canceller.
 9. The acoustic echocancellation device according to claim 1, wherein the first echocanceller produces the first pseudo echo signal with respect to themicrophone disposed at the position closest to the speaker.
 10. Anacoustic echo cancellation method in an acoustic echo cancellationdevice which cancels an acoustic echo component of an input signaloutputted from a microphone, the method comprising: a step of producinga first pseudo echo signal which indicates a component of a reproducedsignal contained in the input signal using an input signal obtained fromthe at least two microphones and the reproduced signal outputted to aspeaker; a step of producing a second pseudo echo signal which indicatesa component of the first pseudo echo signal contained in the at leastone input signal using the at least one input signal outputted from theat least two microphones and the first pseudo echo signal produced bythe first echo canceller; and a step of cancelling an acoustic echocomponent of the at least one input signal using the produced secondpseudo echo signal.
 11. A non-transitory computer readable recordingmedium recording an acoustic echo cancellation program for causing acomputer to function as: a first echo canceller which, using an inputsignal obtained from at least two microphones and a reproduced signaloutputted to a speaker, produces a first pseudo echo signal whichindicates a component of the reproduced signal contained in the inputsignal; and a second echo canceller which, using at least one inputsignal outputted from the at least two microphones and the first pseudoecho signal produced by the first echo canceller, produces a secondpseudo echo signal which indicates a component of the first pseudo echosignal contained in the at least one input signal, and cancels anacoustic echo component of the at least one input signal using theproduced second pseudo echo signal.